The present invention relates to paperboard tubes, and more particularly relates to liquid-resistant paperboard tubes and to methods and devices for making such tubes.
Paperboard tubes are widely used for various purposes. Such tubes are used, for example, as cores onto which paper, film, or textile webs are wound to form rolls. They are also used as containers for various types of products, as load-bearing structures, and as forms for making structures of concrete. Paperboard tubes can achieve great strength and are relatively inexpensive to manufacture. One difficulty associated with them, however, is that exposure of the paperboard to liquid can drastically impair the strength and even the integrity of the tubes. In some uses of paperboard tubes, the tubes may be required to withstand immersion in water or exposure to water-containing compositions for a substantial period of time without losing integrity. Accordingly, paperboard tubes that may be exposed to liquid during storage or use are often treated to make the tubes resistant to liquid. Waxes, silicones, and fluorinated coatings have been used on paperboard tubes for imparting some degree of liquid resistance. These types of treatments, however, typically do not adequately protect the tubes against complete immersion in water for prolonged periods of time.
The present invention addresses the above-noted needs and achieves other advantages, by providing a paperboard tube that is rendered resistant to liquid by coating portions or all of the tube with submicron-sized particles of inorganic material that are treated to be hydrophobic and/or oleophobic. The particles can be applied directly to the paperboard, lodging in surface pores such that the particles adhere to the paperboard. Alternatively, a light coating of a tacky binder or adhesive can first be applied to the paperboard and then the particles can be applied such that they adhere to the binder. Preferably, the particles have a large surface area per gram; in one embodiment, for instance, silica particles are employed having a surface area of about 90-130 m2/g. As a result, the particles create a surface on the paperboard that is highly repellant to liquid.
The particles preferably are applied to the tube by passing the tube through a cloud of the particles with a high enough concentration that the particles completely coat the paperboard surfaces of the tube. Advantageously, the tube can be passed through an enclosure in which the cloud of particles is contained. If desired, the tube can be coated with a tacky binder prior to passing the tube through the enclosure. After the tube exits the enclosure, excess loose particles can be removed from the tube, such as by vacuum, and can be recycled back into the enclosure. The apparatus for treating the tube preferably is operable to maintain the concentration of particles inside the enclosure between predetermined minimum and maximum values.
In accordance with an alternative method of the invention, a liquid-resistant paperboard tube is made by applying a tacky binder to one side of a paperboard ply, wrapping a plurality of paperboard plies one upon another and adhering the plies together to form a tubular body wall, wrapping the paperboard ply having the tacky binder onto the tubular body wall and adhering the ply thereto such that the tacky binder is disposed on an outer surface of the tube, and applying submicron-sized particles of inorganic material to the tube such that the particles adhere to the tacky binder and form a liquid-resistant coating on the outer surface of the tube.